Hi everryone,
basically i want to design a circuit with a supply of 6volts, and a collector current having the value of 5ma. I want to use the transistor TIP31A 219 NPN.

-I dont know how to get the saturation current and the gain of the transistor from the datasheet ?
-In the design of a transistor what value you need and what value you need to take from the datasheet?

The saturation current is not on the datasheet because you can put the transistor into saturation at any current you desire, as long as it is less than the current which destroys the transistor.

In the design of a transistor circuit you start with the highest voltage the transistor can work with, then the highest current, then see if the gain is enough, then see about speed, and that is about as far as I have been.

Oh yeah...after you get done calculating and before you apply power, use Watts Law to be sure nothing will get too hot.

In the design of a transistor circuit you start with the highest voltage the transistor can work with, then the highest current, then see if the gain is enough, then see about speed, and that is about as far as I have been.

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-The highest the voltage of the transistor can work with and the highest the current, the higher the gain?
-Where can I find the maximum possible current from the transistor for base and collector, Im new with datasheet and dont know which one it is?

Saturation is when Vce is very small, but it can never be zero because no transistor is that perfect. Collector current is not "max voltage from supply" because current is not voltage. Collector current is always current from supply for that one transistor.

On the datasheet you provided, maximum voltage is on the first page. It is called, "Collector-emitter voltage".

The maximum continuous collector current and the maximum temporary collector current are also in that first chart on page 1.

The best way to find current gain is in Figure 1, page 3

You apply Watts Law to each part, one at a time. You consider the voltage on the part, the current through the part, and calculate with P=IE. To find if it is too much, you look on the datasheet for each part.

It was someone else that asked the purpose. I do not care the purpose unless you want me to make a drawing for you.

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As I said, I want the collector current from the transistor to change from 5ma to 2.5ma. With a power supply 6Volts. Using a transistor TIP31A.

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That tells me what you want the transistor to do. It doesn't tell me what the purpose of the circuit is or any requirements, such as what is the input you have or want to cause the change from 5mA to 2.5mA?

That tells me what you want the transistor to do. It doesn't tell me what the purpose of the circuit is or any requirements, such as what is the input you have or want to cause the change from 5mA to 2.5mA?

Question:
1. -The highest the voltage of the transistor can work with and the highest the current, the higher the gain?
2. Where can I find the gain Hfe (not the current gain)?
3. Where can I find the IcQ (the current at the Q point)
4. Where can I find the Vceq(The Vce voltage at the Q point)